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Welcome to the second tutorial in our series geared towards Arduino programming on Node.js, using the Johnny-Five framework. Get caught up here.

Johnny-Five is a Firmata based Arduino programming framework. See: JavaScript: Arduino Programming on Node.js.

In the previous tutorial, you created a program that gave you a simple REPL control interface to a servo motor. In this tutorial, you’ll add a slider to control the servo:

New Parts list:

Tutorial Requirements:

One (1) Arduino Microcontroller Board
One (1) 9V wall wart adapter plug or 9v battery harness
Three (3) Jumper cables: red, black, yellow
One (1) Any size Servo
One (1) Slide Potentiometer

First, set up the hardware using this schematic as your guide:

Connect the following…

Servo: Black > GND
Servo: Red > 5v
Servo: Signal > Digital PWM Pin 9
Slider: Black > GND
Slider: Red > 5v
Slider: Signal > Analog 0
Microcontroller > USB
9V Power

Assuming you’re using the actual repo, open up eg/slider-servo-control.js, or follow along here…

slider-servo-control.js

var five = require("../lib/johnny-five.js"),
    board, slider, servo, scalingRange;

board = new five.Board();

board.on("ready", function() {

  scalingRange = [ 0, 170 ];

  slider = new five.Sensor({
    pin: "A0",
    freq: 50
  });

  servo = new five.Servo({
    pin: 9,
    range: scalingRange
  });


  // The slider's value will be scaled to match the servo's movement range

  slider.scale( scalingRange ).on("slide", function( err, value ) {

    servo.move( Math.floor(this.value) );

  });
});

And that’s it!

Run node eg/slider-servo-control.js¹ and try moving the slider up and down — the servo should rotate back and forth between 0-180 degrees (or whatever scalingRange was provided).

Remember to watch this space for more tutorials!

Note: There is a known issue in where the Firmata protocol layer has issues freeing itself on the serial line which results in the program hanging in the ready state. For now, ^C to kill the hanging program and simply run it again.

JavaScript: Arduino Slide Controlling a Servo Tutorial